Summary

Add explicit constructors to some classes in Java Sound APIs which using default constructors.

Problem

Default constructors are not recommended for formal API classes.

Solution

Add the public constructors to the public/non-abstract classes, and protected constructors to the public/abstract classes.

Specification

src/java.desktop/share/classes/javax/sound/midi/VoiceStatus.java    
     public int volume = 0;
+
+    /**
+     * Constructs a {@code VoiceStatus}.
+     */
+    public VoiceStatus() {}
 }

src/java.desktop/share/classes/javax/sound/midi/spi/MidiDeviceProvider.java
    public abstract class MidiDeviceProvider {

+    /**
+     * Constructs a {@code MidiDeviceProvider}.
+     */
+    protected MidiDeviceProvider() {}

src/java.desktop/share/classes/javax/sound/midi/spi/MidiFileReader.java
    public abstract class MidiFileReader {

+    /**
+     * Constructs a {@code MidiFileReader}.
+     */
+    protected MidiFileReader() {}

src/java.desktop/share/classes/javax/sound/midi/spi/MidiFileWriter.java          
    public abstract class MidiFileWriter {

+    /**
+     * Constructs a {@code MidiFileWriter}.
+     */
+    protected MidiFileWriter() {}

src/java.desktop/share/classes/javax/sound/midi/spi/SoundbankReader.java
    public abstract class SoundbankReader {

+    /**
+     * Constructs a {@code SoundbankReader}.
+     */
+    protected SoundbankReader() {}

src/java.desktop/share/classes/javax/sound/sampled/spi/AudioFileReader.java
    public abstract class AudioFileReader {

+    /**
+     * Constructs a {@code AudioFileReader}.
+     */
+    protected AudioFileReader() {}

src/java.desktop/share/classes/javax/sound/sampled/spi/AudioFileWriter.java
    public abstract class AudioFileWriter {

+    /**
+     * Constructs a {@code AudioFileWriter}.
+     */
+    protected AudioFileWriter() {}

src/java.desktop/share/classes/javax/sound/sampled/spi/FormatConversionProvider.java
    public abstract class FormatConversionProvider {

+    /**
+     * Constructs a {@code FormatConversionProvider}.
+     */
+    protected FormatConversionProvider() {}

src/java.desktop/share/classes/javax/sound/sampled/spi/MixerProvider.java
    public abstract class MixerProvider {

+    /**
+     * Constructs a {@code MixerProvider}.
+     */
+    protected MixerProvider() {}

Link for convenience: http://cr.openjdk.java.net/~serb/8250858/webrev.00/